STD. XII Sci. Perfect Biology - II

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2 Written as per the revised syllabus prescribed by the Maharashtra State Board of Secondary and Higher Secondary Education, Pune. STD. XII Sci. Perfect Biology - II Tenth Edition: March 2016 Salient Features Exhaustive coverage of syllabus in Question Answer Format. Topic wise classified Question Answer Format. Covers answers to all Textual Questions. Covers relevant NCERT Questions. Simple and Lucid language. Neat, Labelled and authentic diagrams. Self Evaluative in nature. Multiple Choice Questions for effective preparation. Quick review at the end of each chapter. Concept builder section provided for each chapter. Includes Board Papers of March and October 2013, 2014, 2015 and March Printed at: Repro India Ltd., Mumbai No part of this book may be reproduced or transmitted in any form or by any means, C.D. ROM/Audio Video Cassettes or electronic, mechanical including photocopying; recording or by any information storage and retrieval system without permission in writing from the Publisher _10301_JUP P.O. No

3 Preface In the case of good books, the point is not how many of them you can get through, but rather how many can get through to you. Std. XII Sci. : PERFECT BIOLOGY - II is a complete and thorough guide critically analysed and extensively drafted to boost the students confidence. The book is prepared as per the Maharashtra State Board syllabus and provides answers to all textual questions. Sub-topic wise classified question and answer format of this book helps the student to understand each and every concept thoroughly. Neatly labelled diagrams have been provided wherever required. National Council Of Educational Research And Training (NCERT) questions based on Maharashtra State board syllabus have been provided along with solutions for a better grasp of the concept and preparing the students on a competitive level. Additional information about a concept is provided for better understanding. Multiple choice questions help the students to test their range of preparation and the amount of knowledge on each topic. Quick reviews in the form of charts are provided at the end of every chapter. Additional theory questions have been provided to help the student gain insight on the various levels of theory-based questions. A Concept builder section which includes diagram based questions, match the columns, flow charts and other activities has been provided for each chapter. This will help the students in preparing for various competitive examinations. The journey to create a complete book is strewn with triumphs, failures and near misses. If you think we ve nearly missed something or want to applaud us for our triumphs, we d love to hear from you. Please write to us on : mail@targetpublications.org A book affects eternity; one can never tell where its influence stops. Best of luck to all the aspirants! Yours faithfully, Publisher PAPER

4 PAPER PATTERN There will be one written paper of 70 Marks in Biology. Duration of the paper will be 3 hours. Biology paper will have two parts viz: Part I of 35 marks and Part II of 35 marks There will be two separate answer sheets for both the parts. In the same question paper, each part will have 4 Questions. Sequence of answering the questions can be determined by the students. The paper pattern for Part I and Part II will be as follows: Question 1: There will be 7 multiple choice Questions (MCQs), each carrying one mark. Total marks = 7 Question 2: This will have Questions as A, B and C. In that, Q.A will be based on : Answer in one sentence. There will be 6 Questions each carrying 1 mark Total marks = 6 Q.B will have one Question based on diagrams Total Marks = 2 Q.C will have 4 Questions, each carrying 2 marks Students will have to answer any 2 out of given 4 Questions Total marks = 4 Total Marks (A + B + C) = 12 Question 3: This will have Questions as A and B Q.A will have 3 Questions each carrying 3 marks Students will have to answer any 2 out of given 3 Questions Total Marks = 6 Q.B will have one Question based on diagrams Total Marks = 3 Total Marks (A + B) = 9 Question 4: In this Question, 2 Questions will be asked each carrying 7 marks. Students will have to answer any one out of given 2 Questions Total Marks = 7 Distribution of Marks According to Type of Questions (7 Marks) (12 Marks) (9 Marks) (7 Marks) Type of Questions Marks Marks with option Percentage (%) Objectives Short Answers Brief Answers Total

5 No. Topic Name Topicwise Weightage Marks Without Option Marks With Option 10 Origin and Evolution of Life 11 Chromosomal Basis of Inheritance Genetic Engineering and Genomics Human Health and Diseases 14 Animal Husbandry Circulation 16 Excretion and Osmoregulation Control and Co ordination 18 Human Reproduction Organisms and Environment II Contents Sr. No. Unit Page No. 10 Origin and Evolution of Life 1 11 Chromosomal Basis of Inheritance Genetic Engineering and Genomics Human Health and Diseases Animal Husbandry Circulation Excretion and Osmoregulation Control and Co ordination Human Reproduction Organisms and Environment II 251 Board Question Paper March Board Question Paper October Board Question Paper March Board Question Paper October Board Question Paper March Board Question Paper October Board Question Paper March Note: All Textual questions are represented by * mark. NCERT Questions are represented by # mark.

6 10 Origin and Evolution of Life Chapter 10: Origin and Evolution of Life Syllabus 10.0 Introduction 10.1 Origin of Life 10.2 Organic Evolution 10.3 Origin and Evolution of Human Being 10.0 Introduction Q.1. What is Big Bang? Ans: The single titanic explosion that happened about 15 billion years ago, which resulted in the formation of universe is called Big Bang. Q.2. How did the solar system come into existence? Ans: i. It is presumed that the Universe came into existence with a single titanic explosion called the Big Bang about 15,000 million (15 billion) years ago. ii. With the Big bang, all the matter and tremendous energy came into existence. iii. The fragments of the fire ball expanded and cooled to give rise to many more celestial bodies. iv. In due course of time, this resulted in the formation of our solar system consisting of the sun and planets Origin of Life *Q.3. What kind of atmosphere was existing on primitive earth? Ans: Primitive earth atmosphere was strongly reducing and contained hydrogen, methane, ammonia and water vapours, free oxygen was absent. Q.4. What is protobiogenesis? Which are the different theories of origin of life? Ans: The origin of life on the earth is called protobiogenesis. There are different theories put forth to explain the origin of life. They are: i. Theory of special creation. ii. Cosmozoic theory. iii. Theory of spontaneous generation or Theory of abiogenesis. iv. Theory of biogenesis. Q.5. Explain in brief the Theory of special creation. Ans: i. Theory of special creation is the oldest of all the theories. ii. It was proposed by Spanish monk Father Sudrez. iii. According to this theory, all living beings on the earth were created by God or by a supernatural power. iv. This theory is purely based on religious belief. v. It has no scientific evidence. vi. Therefore, it is not accepted by the scientific world. 1

7 Std. XII Sci.: Perfect Biology II Q.6. Write a short note on Cosmozoic theory. Ans: i. Cosmozoic theory was given by Richter in 1865 and is also known as panspermia theory. ii. According to this theory, life on earth came from a distant planet in the form of spores or microorganisms. iii. It was called cosmozoa or panspermia which were preserved inside meteorites (mass of matter from outer space). iv. These meteorites struck the barren earth to release the cosmozoa and helped in development of various creatures. v. This theory failed to explain the origin of life on the planet, hence it is not accepted. Q.7. What is abiogenesis? Explain the Theory of spontaneous generation or Theory of abiogenesis. Ans: Abiogenesis: It is the hypothetical process by which living organisms are believed to have developed from non living matter. Theory of spontaneous generation: i. It is also called the Theory of autobiogenesis (auto = self, bios = life, genesis = formation). ii. According to this theory, life originated from non living material spontaneously, without any interruption. 2 iii. iv. It was initially putforth by Greek Philosophers in 600 B.C. and was supported by Aristotle. The Greek Philosophers believed that air, water, fire and earth are vital forces or the active principles which have the capacity to transform non living matter into living organisms. v. Louis Pasteur finally disproved the theory of spontaneous generation and gave the scientific explanation that life originated only from pre-existing life or biogenesis. *Q.8. Describe Oparin Haldane theory of chemical origin of life. Ans: The Russian scientist Alexander Ivanovich Oparin (1924) and British scientist J.B.S. Haldane (1929) proposed the Theory of chemical evolution of life. According to this theory, life originated from non-living matter, some three billion years ago, in a primitive atmosphere, through a process of chemical evolution. The entire process of chemical evolution can be divided into the following steps: i. Origin of earth and its primitive atmosphere: a. The origin of life on earth is closely related to the origin of earth itself. b. Evidences suggest that earth originated about 4.6 billion years ago. c. When it was broken from the sun, it was a glowing fire and a rotating cloud of hot gases, vapours of various elements and pieces of rocks and metals called Nebulous. d. This mass of gas exploded with a Big Bang into several small pieces. The earth, as a piece was broken from the sun. e. As the earth was moving away from the sun, it was getting cooled. This led to the condensation of gases. f. The heavy elements like iron, nickel, etc. sank to the centre and formed the solid core of earth. g. The lightest elements like helium, hydrogen, oxygen, nitrogen, carbon, etc. occupied the atmosphere of the earth. h. The geological conditions on the primitive earth about 3600 million years ago were much different from those found today. In fact, the atmosphere of primitive earth was reducing type and there was no free oxygen. ii. Formation of ammonia, water and methane: a. The prebiotic environment had very less resemblance with the present day environment. b. The earth was very hot initially and so the atoms could not combine with each other very easily. c. The primitive earth contained a large amount of hydrogen, nitrogen, carbon and oxygen. d. Of these, hydrogen was very active. e. It combined with nitrogen to form ammonia (NH 3 ), with oxygen to form water (H 2 O); and with carbon to form methane (CH 4 ). f. As the temperature was high, ammonia and methane remained as gases and water as steam. g. As years passed, the temperature of the earth decreased. h. Steam condensed into water which resulted in rain and the earth became cold.

8 iii. iv. Chapter 10: Origin and Evolution of Life i. Water gradually accumulated and this led to the formation of rivers, streams, lakes, seas and oceans. j. Compounds like ammonia, methane, etc. were dissolved in rain water and accumulated in the sea. Thus, the first chemicals formed on the earth were water, ammonia, methane, etc. Synthesis of simple organic compounds: a. The next step in molecular evolution was the formation of micromolecules. b. As the earth surface considerably cooled, the highly reactive free radicals CH and CH 2 condensed to form a variety of both saturated and unsaturated hydrocarbons. c. The simple inorganic molecules of the oceanic water interacted with one another to form simple organic molecules such as sugar, fatty acids, glycerol, amino acids, purines and pyrimidines. d. The energy for these reactions was provided by the electrical discharges (lightning), ultraviolet rays (solar radiations), volcanic activities and decay of radioactive elements CH 4 + NH 3 + H 2 O amino acids. CH 4 + HCN + NH 3 + H 2 O purines + pyrimidines CH 4 + H 2 O sugar + glycerol + fatty acids. Haldane described the sea containing molecules of these organic substances in abundance as the hot dilute soup or primitive broth. Formation of complex organic compounds: The hot dilute soup was sterile and oxygen free. Simple organic substances came together in increasing numbers. They colloided, reacted and aggregated forming new complex molecules such as polysaccharides, fats, proteins, nucleosides and nucleotides. The protein molecules made their existence by polymerization of amino acids. These proteins showed enzymatic reaction and were called protoproteins. Due to their enzymatic nature, these proteins accelerated the rate of other chemical reactions. The formation of protein molecules is considered as a landmark in the origin of life. v. Formation of nucleic acid: The next step in chemical evolution was formation of nucleic acid. It was formed by the aggregation of phosphoric acid, sugar, purines and pyrimidines. They were linked in various combinations to form different types of nucleotides. Thousands of nucleotides joined together to form nucleic acid. It acquired self replication ability, which is a fundamental property of living forms. vi. vii. Formation of Protobiont or precells: The nucleic acid along with inorganic and organic molecules formed the first form of life and were called protobionts or precells. The proteins formed colloidal hydrophilic complexes surrounded by water molecules. Oparin and Sydney Fox demonstrated the formation of this aqueous suspensions of polymers. Oparin called these aggregates as Coacervates, while Sydney Fox called them Protenoids or Microspheres. Formation of First Cell: The nucleic acids in pre-cells had the capacity to multiply but gradually it started directing a series of chemical reactions like protein synthesis. That was the significant step in the transformation of pre-cell into a cell. This chemical evolution gave rise to the biological evolution. viii. Biological evolution: The first cells or primitive cells were marine and heterotrophic in nature. They obtained their food from the surrounding areas. Growth and multiplication of these cells caused depletion in the food and increase in CO 2 due to fermentation. These were the favourable circumstances for mutation, which resulted in the development of chromophores. The chromophores had the ability to trap light energy and convert it into chemical energy. This event helped in the transformation of heterotrophs into autotrophs. Due to release of oxygen as a byproduct of photosynthesis, the primitive reducing atmosphere was slowly and gradually converted into an oxidizing atmosphere. 3

9 Std. XII Sci.: Perfect Biology II Q.9. Describe the Coacervate theory of Oparin. Ans: Coacervate theory of Oparin: i. In 1938, Oparin performed an experiment in which he explained that the formation of protein molecule was a very crucial event in the course of chemical evolution. ii. He also tried to explain the transformation of non-living substances into living forms. iii. He suggested the formation of coacervates. iv. Thus, Oparin suggested that they might have originated from the primitive earth, substances from which the first cell like forms might have come into existence. v. He called them Protobionts or Eubionts. Q.10. Describe Microsphere theory of Sydney Fox. Ans: i. In 1959, Dr. Sydney Fox studied Oparin s coacervate theory and performed the experiments by stimulating prebiotic environmental conditions in the laboratory. ii. In his experiments, he heated the amino acids which polymerized into protein like droplet called proteinoids. iii. These aggregated into spherical colloidal droplets which were called microspheres. Assembly of organic compounds Q.11. Give an account of Urey and Miller s experiment. Ans: i. Stanley Miller and Urey designed an apparatus and created conditions similar to primitive atmosphere. ii. The apparatus had a spark chamber with two tungsten electrodes, flask for boiling water, side tube connected to a vacuum pump condenser and U-shaped trap. iii. The electric discharge was created by using electrodes in a spark chamber containing methane, ammonia, hydrogen and water vapours in the ratio 1:2:2 without air. This was done to create prebiotic environment. iv. The flask containing water was heated to provide water vapour. v. They passed the mixture through a condenser. vi. They circulated the gases continuously in this way for one week and then analysed the chemical composition of the liquid inside the apparatus. Observation: They observed a large number of simple organic compounds including some amino acids such as alanine, glycine and aspartic acid. Conclusions: All these complex organic compounds including amino acids, were synthesized non-enzymatically. This proved that complex organic compounds could be synthesized in reducing atmosphere without the help of enzymes and thus supported the Theory of chemical evolution. Connection to vacuum pump & gas supply to remove original air & introduce gas mixture Water vapour Spark Discharge Condensation of hot vapour Water vapour Gas flask (reducing atmosphere) Electrode Hot water Condenser Cold water Sparker H 2 NH 3 CH 4 Vapour Boiling water Hot plate Stop cock for drawing liquid for test H 2 O containing organic compounds at end of experimental run Miller and Urey Experiment 4

10 Chapter 10: Origin and Evolution of Life 10.2 Organic Evolution *Q.12.What is meant by organic evolution? [Oct 15] Ans: Organic evolution is a slow, gradual, continuous and irreversible changes through which the present day complex forms have descended from their simple, pre-existing forms of the past. *Q.13. Describe Darwin s theory of natural selection. State the objections raised against this theory. Ans: Charles R. Darwin was a British biologist. He postulated the Theory of origin of species by natural selection. Principles of Darwinism: Darwin s theory of organic evolution by natural selection is based on the following principles: i. Over production or prodigality of production: All organisms have a natural tendency to over produce. If this tendency is not checked, then even a single species of a plant or animal will occupy the entire space available on the earth. ii. Struggle for existence: Organisms multiply in geometric ratio, but space and food remain constant leading to competition for survival. Increase in the number of species leads to a competition called struggle for existence. iii. Variations and Heredity: The differences which occur between the closely related organisms are called variations. It is universal law of nature. Variations may be favourable or unfavourable. iv. Survival of the fittest or natural selection: According to Darwin, in the struggle for existence, the fittest individuals survive and reproduce, while the unfit individuals perish. v. Origin of new species: According Darwin, useful variations appear in every generation and are inherited from one generation to another. Objections to Darwin s natural selection theory: i. Natural selection theory explained survival of the fittest but not arrival of the fittest. ii. Darwin did not take into account the hereditary principles. iii. He could not provide a satisfactory explanation for the cause, origin and inheritance of variations. iv. Certain useless characters are also inherited. He could not explain the inheritance of useless variations. v. He was unable to differentiate variations as hereditary and environmental variations. *Q.14.Write a note on Struggle for existence. Ans: Struggle for existence: According to Darwin, individuals multiply in geometric ratio, but the space and food remain constant. This leads to competition for getting requirements of life. This competition is called Struggle for existence. The struggle may be intra-specific, inter-specific or environmental. i. Intra-specific struggle: It is the competition among the individuals of the same species. This type of struggle is very severe, because the need and approach of all competing organisms is precisely same. e.g. struggle between cow and cow, horse and horse, deer and deer, etc. for getting grass. ii. Inter-specific struggle: It is the struggle between the organisms of different species living together. Individuals of one species compete with other species for food, shelter and breeding place. e.g. Struggle between cow, horse nd deer for getting grass. iii. Environmental struggle: It is the struggle of all living forms against adverse environmental conditions, i.e. against natural calamities like extreme heat or cold, drought, storms, earthquakes, volcanic eruptions etc. 5

11 Std. XII Sci.: Perfect Biology II *Q.15.Describe the concept of Survival of the fittest. [Oct 15] Ans: Survival of the fittest or Natural selection: i. The organisms having favourable variations succeed in the struggle for existence. ii. The organisms with unfavourable variations are unfit to survive and they perish. 6 iii. iv. This means survival of the fittest. Nature selects the organisms with favourable variations and these are fittest to survive, hence, the theory is known as Theory of Natural selection. Q.16. What are the important postulates of Hugo De Vries Mutation theory? Ans: Mutation theory of Hugo de Vries states that evolution is a jerky process. New varieties and species are formed by mutations or discontinuous variations that function as raw material for evolution. Salient features of Mutation Theory are: i. Mutations are the raw material for evolution. ii. Mutations appear suddenly and become operational immediately. iii. The same type of mutations can appear in a number of individuals of a species. iv. Since they are changes in genetic material, all mutations are potentially inheritable. Somatic mutations have least chances of getting transmitted. v. Mutations are unpredictable and appear in all conceivable directions. vi. Useful mutations are selected by nature. Lethal mutations get eliminated. vii. Sometimes, useless and less harmful mutations continue to persist in the progeny. viii. Accumulation of variations produce new species. ix. Sometimes, a new species is produced from a single mutation. x. All in all evolution is a jerky and discontinuous process. Q.17. What were the objections to Hugo de-vries theory of mutation? Ans: Objections to Hugo de-vries theory of mutation: i. Sudden appearance of large discontinuous variations observed by Hugo de Vries were not really gene mutations, but were actually due to chromosomal aberrations that have little value in evolution. ii. Mutation is actually a change in structure of gene and brings about a minor variation. iii. iv. Rate of mutation is very slow, i.e. one per million or several millions. Mutation is one of the many agents of evolution. Gene mutations are the raw material on which natural selection can act to bring about evolutionary changes. Modern synthetic Theory of Evolution *Q.18. Give the three key factors of the modern synthetic theory of evolution. Ans: Genetic variation, natural selection and isolation are the key factors of modern synthetic theory of evolution. *Q.19. Explain modern synthetic theory of evolution. Ans: Julian Huxley proposed term modern synthesis. This theory was based on the work of Dobzansky. The salient features are as follows. i. According to the Modern synthetic theory of evolution, population is considered as a unit of evolution because new species are evolved from a population and not from a single individual. ii. A group of similar individuals interbreeding among themselves, occupying a geographical area is called genetic population or Mendelian population. iii. The sum total of genes of all individuals of interbreeding population is called gene pool. iv. Every gene pool has different genes, each having their own specific gene frequencies. v. The Modern synthetic theory is based on three main concepts, i.e. Genetic variations, Natural selection and Isolation. a. Genetic variation: 1. It is the change in gene and gene frequencies. 2. It is the raw material for evolution. 3. Genetic variation in populations is caused by Gene mutations, Gene flow, Genetic recombination, Genetic drift and Chromosomal aberrations.

12 Chapter 10: Origin and Evolution of Life b. Natural selection: 1. It brings about evolutionary changes by favouring differential reproduction of genes that bring about changes in gene frequency from one generation to another. 2. Natural selection invariably encourages those genes that assure highest degree of adaptive efficiency between population and its environment. c. Isolation: 1. Interbreeding does not occur between two isolated groups. 2. Each group may develop a set of new traits that lead to evolutionary changes and towards formation of new species. *Q.20. Define Gene pool. Ans: The sum total of genes of all individuals of interbreeding population is called gene pool. *Q.21. Explain the terms: Gene pool and Gene frequency. Ans: Gene pool: i. It refers to the sum total of genes of all individuals of interbreeding population. ii. Changes in gene pool results in evolution. Gene frequency: The proportion of an allele in the gene pool as compared with other alleles at the same locus is called gene frequency. *Q.22. Write a note on Genetic drift. Ans: i. Any alteration in allele frequency in the natural population by pure chance is called genetic drift. ii. For example, elimination of a particular allele from a population due to events like accidental death prior to mating of an organism. iii. Genetic drift occurs when the sole possessor of a particular allele is removed from the population. iv. It is also called Sewall Wright effect. Q.23. Define: i. Gene mutations ii. Mutagens Ans: i. Gene mutations: Changes in the chemical make-up of a gene is called gene mutation. ii. Mutagens: Mutation causing agents are called mutagens. *Q.24. Name the mechanism by which new alleles appear in a population. Ans: Gene mutation is the mechanism by which new alleles appear in a population. Q.25. State the important factors that can alter the gene frequency. Ans: Following factors alter the gene frequency in genetic equilibrium: i. Gene mutation: Changes in the chemical make up of a gene is called gene mutation or point mutation. These mutations are the cause for new alleles that introduce variations in the gene pool and it accounts for the change in gene frequency. ii. Gene flow: Transfer of genes between populations that differ genetically from one another is called gene flow. For e.g. When animals migrate from an area to another, they contribute their genes to the gene pool of that area and hence a change in gene frequency. iii. Genetic recombination: In sexually reproducing organisms, during gametogenesis, the homologous chromosomes exchange genetic material by the process of crossing over. This produces new combinations and the phenomenon is called genetic recombination. It adds variability to individuals. 7

13 Std. XII Sci.: Perfect Biology II 8 iv. Genetic drift: Any alteration in allele frequency, in the natural population by pure chance is called genetic drift. For e.g. elimination of a particular allele from a population due to events like accidental death prior to mating of an organism, i.e. the sole possessor of particular allele. Smaller populations have greater chances for genetic drift. It is also called Sewall Wright effect. v. Chromosomal aberrations: It refers to the structural alterations in a chromosome causing changes in the gene arrangement. e.g., deletion, duplication, translocation and inversion. They also cause variations in the Mendelian populations. Q.26. What is gene flow? [Mar 14] Ans: Transfer of genes between population that differ genetically from one another is called gene flow. Q.27. How does gene flow bring about a change in gene frequency? Ans: i. Gene flow is also called as gene migration. ii. When a section of population migrates to another population, gene pool of both the populations change, as some alleles are lost from first population, while they are added to second population. iii. When animals migrate from an area to another, they contribute their genes to the gene pool of that area and hence a change in gene frequency. Q.28. Explain natural selection with a suitable example. Ans: Natural selection: It is a fundamental and the only operating mechanism of evolution. It is a link between changes in the environment and genetic variations of the species attempting to survive and reproduce. It brings about evolutionary changes by favouring differential reproduction of genes that brings about changes in gene frequency from one generation to another. Natural selection invariably encourages those genes that assure highest degree of adaptive efficiency between population and its environment. The natural selection in action can be appreciated by studying the example of Industrial melanism. Example: Industrial Melanism: i. Industrial Melanism is one of the best examples for natural selection in action which refers to development of dark coloured peppered moths in response to air pollution during the industrial revolution in Great Britain. ii. The dark coloured moths developed as a result of random mutation. iii. It was first reported by scientist Kettlewell. iv. Before the industrial revolution (1845), light coloured peppered moths called Biston betularia were prevalent in very high numbers. v. The peppered moths are nocturnal in habit. vi. During daytime, they rest on the tree trunk. vii. Their pale body colour camouflaged well with the lichen covered trees that helped them to escape from the predatory birds. viii. On the contrary, the Black coloured moth called Biston carbonaria, resting on lichen covered tree trunks were very conspicuous and were easy victims for the predatory birds, hence they were rare. ix. During the industrial revolution, large number of industries came up in Great Britain. x. The industries released black sooty smoke that killed the lichens growing on trees and turned the trees black due to the sooty deposits.

14 Chapter 10: Origin and Evolution of Life Dark coloured moth Light coloured moth Dark coloured moth Light coloured moth Before industrial revolution After industrial revolution xi. Isolation This change became an advantage to the black coloured moths that camouflaged well with the black tree trunks and their population increased, while the pale coloured moths became easy victims to predatory birds and so their population drastically reduced. Thus, natural selection has resulted in the establishment of a phenotypic trait in changing the environmental conditions. Q.29. Define isolation. Describe the types of isolation. Ans: Isolation: Separation of a single population into several sub-units is called Isolation. Interbreeding does not occur between isolated groups. Each group may develop a set of new traits that lead to evolutionary changes and towards formation of new species. The isolating mechanisms are of two types: i. Geographical isolation: a. It occurs when an original population is separated into two or more groups by geographical barriers such as river, mountain, ocean, island formation, forests, etc. b. The separated groups are exposed to different kinds of environmental factors. Hence, each group acquires variations by developing mutations, recombination, etc. c. These variations are processed by natural selection. This leads to progressive genetic divergence. The separated populations develop distinct gene pool and they do not interbreed. Thus, the species are formed by geographical isolation. d. The classic example of geographical isolation is that of Darwin s finches. e. Example: Darwin s finches living on Galapagos islands differ not only among themselves but also from mainland finches in size, colour, beak and food habits. ii. Reproductive isolation: a. Reproductive isolation is brought about by the change in genetic material, gene pool and structure of genital organs. b. It prevents interbreeding between populations whether they are geographically isolated or living close together. Q.30. Describe various types of premating isolating mechanisms. Ans: Pre-mating or pre-zygotic isolating mechanisms: i. Habitat isolation: In this isolation, members of a population living in the same region occupy different habitat. Thus, potential mates do not meet. ii. Seasonal isolation: In this isolation, members of a population attain sexual maturity at different times, thus preventing interbreeding. 9

15 Std. XII Sci.: Perfect Biology II iii. iv. Ethological isolation: In this isolation, members of two populations have different mating behaviours. This prevents interbreeding. Mechanical isolation: In this isolation, the members of two populations have difference in the structure of reproductive organs. So, interbreeding is not possible. Q.31. What are the various types of post mating isolating mechanisms? Ans: Post-mating or post zygotic isolating mechanisms are: i. Gamete mortality: Sperm transfer takes place but egg is not fertilized. ii. Zygote mortality: Egg is fertilized but zygote dies. iii. Hybrid sterility: Hybrids are sterile. Biological Evidences Q.32. Define: i. Palaeontology Ans: The scientific study of life of the geologic past involving the fossils of plants, animals and microbes is called Palaeontology. 10 ii. Fossils Ans: Fossils are the dead remains or traces of animals, plants, and other organisms from the remote past. Q.33. Which are the evidences that support the process of evolution? Ans: Process of evolution is supported by evidences provided by various branches of biology. They are: i. Palaeontology ii. Comparative Anatomy iii. Embryology iv. Genetics *Q.34. Describe any two biological evidences of evolution. Ans: i. Palaeontological evidence of evolution. a. Fossils are defined as the dead remains of plants and animals that lived in the past in various geological layers. b. Unlike the evidences from other branches of biology, evidence from fossils are sound, direct and reliable. c. Fossils are described as the true witnesses or documents of evolution. d. The development in the field of Geology reveals that the primitive forms of organisms occupy the lower layers and the advanced forms occupy the upper layers of the earth during fossilization. e. Fossils are found in sedimentary rocks, amber, volcanic gas, ice, peat bogs and soil, etc. ii. Anatomical evidences of evolution: The study of internal structure of an organism is called anatomy. a. Anatomical evidences are of three types, viz. Homologous organs, Analogous organs and Vestigial organs. b. Though the animals belonging to different groups vary greatly in their external morphology, yet they show the same structural plan internally, i.e. in their anatomy. c. The organs having common origin but performing different functions are known as homologous organs and the phenomenon is called homology. Homology is the result of divergent evolution. Homology of organs indicate their common ancestry. e.g. forelimbs of whales, bat, birds, amphibians and humans as all have basic anatomical structure with bones humerus, radius ulna, carpals, meta carpals and phalanges. 1. Analogous organs i. The organs having different origin but performing same function are called analogous organs and the phenomenon is called analogy. e.g. wings of butterfly (insects) and birds. ii. Analogy is the result of convergent evolution.

16 Chapter 10: Origin and Evolution of Life 2. Vestigial organs Organs are functionless and rudimentary to the possessor but were functional in the ancestors and are also functional in related animals. e.g. i. Caecum and vermiform appendix ii. Nictitating membrane iii. Coccyx or tail vertebrae Q.35. Write about the categories of fossils. Ans: The categories of fossils are as follows: i. Actual remains: These are the most common type of fossils. Actual remains are generally formed in the deep oceans. Whenever the plants or animals die, their dead bodies sink to the bottom of the sea. Here, either the entire body or its hard parts get surrounded by minerals forming the parts of stones. Another way of formation of actual remains is incorporation of the entire body or part of the body in the ice. ii. Moulds and Casts: A mould is an impression of the body parts left on the soft mud of the oceanic floor. When the cavities of the mould get filled with minerals, it hardens into stones and forms cast. Q.36. State the significance of palaeontological evidences. Ans: i. It is useful in reconstructing the phylogeny, i.e. the evolutionary history of the organisms. ii. Palaeontology helps in studying various other forms and structures of extinct animals. iii. Fossils are important tools which help in understanding the habit and habitat of the extinct organisms. iv. Fossil records provide the connecting links between two groups of organisms. Q.37. Why is Archaeopteryx called connecting link? Ans: Organisms showing characters of two groups (kingdoms, phyla, classes, etc.) are called connecting links between the two groups. Archaeopteryx shows characters of birds as well as of reptiles. Avian characters of Archaeopteryx: i. It has skull bones completely fused: cranium rounded with large orbits and a single condyle. ii. Jaws modified into beak. iii. Forelimbs modified into wings. iv. Limb bones have their first toe opposable. v. Foot with clawed digits. vi. Feathery exoskeleton Reptilian characters of Archaeopteryx: i. Jaw with homodont teeth. ii. Ribs with single head. iii. Abdominal ribs somewhat like those seen in crocodiles. iv. Forelimbs modified into wings and three digits ending in distinct claws. v. The hind limb had four digits ending with claws. vi. Long tail. So, the Archaeopteryx is a connecting link between classes, Aves and Reptilia. 11

17 Std. XII Sci.: Perfect Biology II Wing feathers of remiges Scapula Sclerotic bones in orbit Teeth in beak Free caudial vertebrae in lizardlike tail Furcula Free clawed finger III II I I IV II III Clawed toes Coracoid Humerus Free metacarpals Radius Ulna Ribs Tarso metacarpals Rectrices of tail feathers Fossil of Archaeopteryx *Q.38. Name the organism which is connecting link between reptiles and aves. Ans: Archaeopteryx is the connecting link between reptiles and aves. Q.39. Describe in brief homologous organs to support evolution. Ans: Humerus Radius ulna Carpals Metacarpal Phalanges Bat Whale Frog Horse Bird Man Homology of Vertebrate limbs to show adaptive radiation 12 i. The organs or parts that are similar in basic structural plan of development but different in functions are called homologous organs. ii. A study of hand of man, fins of whale, wings of bird, forelimb of horse suggest that all these organs of the animals belonging to different groups show similar internal organization, i.e. presence of humerus, radio-ulna, carpals, metacarpals and phalanges. iii. However, the external appearance of hand of man, fins of whale, wing of bird, forelimb of horse is different. iv. Not only that, these organs perform different functions, hand of man for gripping, wings of bird for flying, forelimb of horse for running, fins of whale for swimming. v. The study of homologous organs suggest that these animals belonging to different groups have descended from a common ancestor. In other words, they have evolved from a common ancestor.

18 Chapter 10: Origin and Evolution of Life Q.40. Write a short note on Analogous organs. Ans: Wing of Insect Wing of Pterodactyl Wing of Bird Wing of Bat i. The phenomenon of occurrence of analogous organs is called analogy. ii. Organs which are structurally dissimilar and functionally similar are called analogous organs. eg. wings of insects and wings of birds are used for flying, but wings of insects are the expansions of exoskeleton, whereas wings of birds are modification of forelimbs for flying. iii. Organs which exhibit similar external appearance, perform same function, but differ in their internal organisation are analogous organs. eg. wings of insects and wings of birds. iv. Butterfly wings and bat wings serve the same function of flying and wings in both type of animals are flat, but structurally they differ very much. Butterfly wings have chitinous deposition without bones. Bat wings have the typical basic plan of limb bones, viz. humerus, radius, ulna, carpals, metacarpals and phalanges. Q.41. Differentiate between Homologous and Analogous organs. Ans: No. Homologous organs Analogous Organs i. Homologous organs have common developmental origin. ii. They have similar basic structure and may have different functions. e.g. Wings of birds and forelimbs of humans, heart of all vertebrates. iii. Homologous organs lead to divergent evolution. Q.42. Explain in brief vestigial organs to support evolution. Ans: Analogous organs have different developmental origin. They have different structure but perform similar functions. e.g. Wings of birds and wings of insects. Analogous organs lead to convergent evolution. Sacrum Vermiform Appendix Vestigial organs Nictitating membrane i. Vestigial organs are those, which are present in reduced form in the organism and are functionless. Hence, their presence is not required. ii. However, they continue to exist before they degenerate and disappear in the process of evolution. iii. They were well developed and functional in the ancestors, but became reduced and functionless in the present day organisms due to change in habitat and habit. 13

19 Std. XII Sci.: Perfect Biology II iv. The study of vestigial organs suggests the process of evolution. It explains that present organisms have evolved from the ancestors, slowly, gradually and orderly. v. In man, presence of the following organs indicates its use in the past: a. Caecum and vermiform appendix: It is still seen in man as a functionless organ. It helps in cellulose digestion in herbivorous mammals. b. Nictitating membrane: It is present in the eyes of humans and is a remnant of the third eyelid. c. Coccyx or tail vertebrae: It is the remnant of a tail in human. Q.43. Define Developmental biology. Ans: It is a branch of biology which deals with the development of an organism from the egg stage to adult stage. *Q.44.Explain embryological evidences of evolution. Ans: All living organisms in their early developmental stages show presence of the following distinct features: I I I I I I I I II II II II II II II II 14 III Fish III Salamander III Tortoise III Chick Embryological Evidences i. Development in sexually reproducing organisms begins from a single diploid cell stage, i.e. a fertilized egg or zygote. ii. Zygote undergoes cleavage, blastulation and gastrulation. At the end of gastrulation, three germ layers are formed which give rise to various organs and organ systems. iii. Embryos of different vertebrates, i.e. from fishes to mammals look alike particularly with reference to gill slits, gill clefts and tail. From these similarities, it can be concluded that all these groups have evolved from the same ancestral stock. Q.45. Write a note on molecular evidences showing evolution. Ans: i. Cell forms the basic structural and functional unit of life in all living organisms. ii. All organisms show presence of endoplasmic reticulum, Golgi bodies, mitochondria as cell organelles. iii. Similarities in proteins and genes performing a given function among diverse organisms proves common ancestry. iv. Basic processes like catabolic activities to liberate energy, synthesis of macromolecules like proteins, carbohydrates and nucleic acids, etc. are similar. ATP is the energy currency in all the living organisms. All these are molecular evidences favouring evolution. III Pig III Calf III Rabbit III Man

20 Chapter 10: Origin and Evolution of Life Q.46. What is geological time scale? Ans: Geological time scale is the arrangement of major divisions of geological time into eras, periods and epochs on the time scale, in order of their age. Q.47. Explain the division of timescale. Ans: i. Geological time scale is divided on the basis of significant events occurred in the organization of organisms. ii. Major divisions of time scale are called eras. iii. Eras are divided into periods and periods into epochs. Q.48. Enlist the eras in geological time scale. Ans: i. Azoic ii. Archeozoic iii. Proterozoic iv. Palaeozoic v. Mesozoic vi. Cenozoic Adaptive radiation Q.49. Define adaptive radiation. [Oct 14] Ans: The process of evolution which results in transformation of original species to many different varieties is called adaptive radiation. Q.50. Give examples of adaptive radiation. Ans: i. Darwin s finches: Darwin s observed many different varieties of finches in the same island. All varieties had evolved from original seed eating finches. With alteration in beaks, some become insectivorous and some vegetarian. ii. Variety of beaks of finches that Darwin found in Galapagos Island Marsupials of Australia: In Australia, Kangaroo is the most known marsupial mammal. Within the Australian continent, many different marsupials or pouched animals are seen. These evolved from a common ancestral stock. A variety of placental mammals have evolved which appear similar to a corresponding marsupial. Adaptive radiation is also called parallel evolution. Q.51. How do Darwin s finches explain adaptive radiation? Ans: i. Darwin s finches of different islands showed variations, but yet they closely resembled one another. ii. These finches radiated to different geographical areas where they had undergone profound adaptive changes, especially in the form of beaks. iii. Living in isolation for long, new kinds of finches have evolved which could survive better in the new environment or new habitats. iv. Adaptive radiation is the process of evolution starting from a point (of common ancestor) in a geographical area and literally radiating to other geographical areas (habitats) leading to formation of new species adapted to new habitats and new ways of life. Q.52. Explain Hardy-Weinberg s principle as binomial expansion. Ans: i. G.H. Hardy and Weinberg independently developed a method, to relate evolutionary changes and population genetics. ii. It is known as Hardy-Weinberg equilibrium principle. The principle states that allele frequencies in a population of sexually reproducing organisms are stable and remain constant (genetic equilibrium) from generation to generation; the sum total of all the allele frequencies is one. 15

21 Std. XII Sci.: Perfect Biology II 16 iii. iv. Let us assume that a gene has two alleles A (dominant) and a (recessive) and their frequencies are named p and q respectively. a. The frequency of AA individuals in a population is p 2, i.e. the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual. b. Similarly, the frequency of aa individuals in a population is q 2. c. The frequency of Aa individuals is 2 pq. Hence, p 2 + 2pq + 2q 2 = 1, which is the binomial expansion of (p + q ) 2. When the frequency measured differs from the expected values, the difference indicates the extent of evolutionary change. v. Five factors are known to affect Hardy-Weinberg equilibrium. They are: a. Gene migration b. Genetic drift c. Mutation d. Genetic recombination e. Natural selection Q.53. Give the graphical representation of Hardy-Weinberg s principle in the form of Punnet Square. [Oct 13] Ans: Graphical representation of Hardy Weinberg s principle in the form of Punnet Square: Hybrid Aa A(p) a(q) 10.3 Origin and Evolution of Human Being Hybrid A(p) AA (p 2 ) Aa (pq) Q.54. Who made the first attempt to explain the origin of man and established that apes are closest relatives of man? Ans: Thomas Huxley made the first attempt to explain the origin of man and established that apes are closest relatives of man. Q.55. Write a note on Lemurs. Ans: i. ii. Aa a(q) Aa (pq) aa (q 2 ) Lemurs are small arboreal animals mainly found in Madagascar. They have grasping hands and feet, flat snouts, large eyes facing more in front than lateral sides and long bushy tails. Q.56. Write a note on Tarsiers. Ans: i. Tarsiers are arboreal, nocturnal, insectivorous primates found on islands of East Indies. ii. Their eyes are large, directed forward and have binocular vision. iii. The limbs have five digits with adhesive pads and most of the digits have nails, except the second and third toes of hind limb bear claws. iv. Their hind limbs are longer with elongated tarsals. From tarsier like ancestor, evolved the earliest anthropoids. Q.57. Describe the Anthropoids. Ans: Anthropoids or sub-order anthropoidae includes the following animals: i. New world monkeys: They have flat noses with widely separated nostrils, long prehensile tails and primitive dentition, 36 teeth. They are found in South and Central America. e.g. squirrel monkey, spider monkey, etc. ii. Old world monkeys: They have narrow noses, short non-prehensile tails and 32 teeth. The old world monkeys are found in tropical regions of Africa and Asia. e.g. baboons, macaques, langurs, etc. iii. Hominoidea (Hominoids): It includes apes and man. Probably they have evolved simultaneously and from the common ancestors. Modern apes such as gibbons, orangutans, chimpanzees and gorillas have originated from primitive apes.

22 Chapter 10: Origin and Evolution of Life *Q.58. Write the names of animals which belong to order primates. Ans: Lemurs, Lorises, Tarsiers, New world monkeys, Old world monkeys, Apes and Man belong to order primates. Q.59. Arrange the following stages of the human evolution in the order of their increasing cranial capacity. A. Neanderthal man [Mar 13] B. Cro-Magnon man C. Homo erectus D. Homo habilis Ans: Correct sequence is as follows: D. Homo habilis ( cc) C. Homo erectus ( cc) A. Neanderthal man (1450 cc) B. Cro-Magnon man (1600 cc) Q.60. Compare the characteristics of Australopithecus to Modern man. Ans: i. The skull of African ape-man resembled the skull of an ape. Its volume was about that of man s skull, its cranial capacity being about 600 c.c. ii. Jaws and teeth were like that of man. iii. Its forehead was also like that of man. iv. The structure of its pelvic girdle showed that it could walk erect. The Australopithecus appears to have been animal hunting, flesh eating and shell cracking primate. Zoologist believe that these animals were the ancestors of man or a man with ape brain. Q.61. State the advantages of erect posture and large brain volume which are beneficial to humans over other primates. Ans: Erect Posture: The erect posture helped the man in the following ways : i. Because of this, man is able to have bipedal mode of locomotion. ii. The feet of man form a kind of stable platform which help him to walk erect and balance properly. iii. The hands of man are shorter and free to handle work. iv. The thumb of man is better developed. The thumb closes in on the other fingers of hand. v. Man can use his hands more delicately. This type of thumb is called opposable. vi. Man can handle even small tools and other instruments because of the position of thumbs and fingers with great dextricity. Large Brain Size: Following are the advantages of large brain size: i. Brain becomes more developed. Its brain ratio is more than the others as compared to body weight. ii. Large sized brain-greater intelligence, thinking power and correlation of facts and events. iii. Shifting of information. iv. Capacity of reasoning developed. v. Senses became more powerful. vi. Reflexes became more prominent. vii. In fact, it is the hand and the brain that made man a super animal. *Q.62. Write note on Java man and Peking man. Ans: i. Java man: a. Homo erectus fossils of Java were called Java man. b. Its fossils were first obtained by Dubois (1891) and these were named Pithecanthropus erectus. c. The cranial capacity was about 940cc. d. The chin was absent, bony eyebrow ridge was present. e. It was more ape like than man like, hence it is also called as Java Ape Man. f. However, he might have made use of fire. g. The original species of Pithecanthropus erectus has been named as Homo erectus erectus by Mayer (1950). h. It lived in the middle pleistocene epoch about 5,00,000 years ago. i. It was about five feet in height and walked erect. j. Its face was prognathous and the jaws were massive with huge teeth. 17